1. Field of the Invention
This invention relates to an inkjet ink composition and printed matters created by using the inkjet ink composition.
2. Description of the Related Art
In recent years however, an on-demand printer which is capable of quickly coping with the diversification of needs and of minimizing stocks has been increasingly utilized. As for such an on-demand printer, an electrophotographic printer where a toner or a liquid toner is employed as well as an inkjet printer which is capable of achieving high-velocity and high-quality printing are expected to be useful. In the case of the inkjet printer, it is possible to handle a solvent type ink in a closed system until the ink is discharged onto the surface of printing matter. Moreover, since the ink can be effectively utilized without substantially generating redundant ink, it is possible to alleviate the problem of environmental contamination.
Further, a photosensitive inkjet ink as well as an inkjet printer system employing the photosensitive inkjet ink are now taken notice of. As for the photosensitive inkjet ink useful in this case, an ink composition comprising, for example, a radical polymeric monomer, a photopolymerization initiator and a pigment is typically employed. It is also proposed to employ a photopolymerizable photosensitive ink which comprises a cationic polymerizable monomer, a photocation-generating agent and a pigment. According to these techniques, since an ink layer formed using such photosensitive inks can be readily nonfluidized by the irradiation of light, it is possible to obtain a printed matter which is unharmful and of high-quality.
On the other hand, in the case of the inkjet recording apparatus which is adapted to be employed in such a quick-drying printing as described above, the printing heads are generally linearly arrayed for accelerating the printing, thus making it possible to perform the printing with one pass over a printing surface. Therefore, any error in the delivery of ink would lead to the generation of a linear defective printing (missing of printing) on the printed surface. Therefore, it is indispensable to obviate as much as possible the generation of such an error zero. Namely, it is required for an ink to be employed in this case that the ink is made up of materials which are excellent in stability, thereby making it possible to achieve very high printing precision and delivery stability. Such requirements are generally fulfilled by the employment of pigment particles having an extremely fine average particle diameter and by the stabilization of the bond between the pigment particles and a dispersing agent.
Since the aforementioned ink of cationic polymerization type is capable of enhancing the adhesion of the radical polymerization type ink as well as capable of modifying the low sensitivity of the radical polymerization type ink that may result from oxygen inhibition, the demand for this cationic polymerization type ink is expected to be increased in future. These photo-curing type inkjet inks however are accompanied with a problem that when pigment is employed as a coloring material, the dispersibility of the ink would become unstable with time. This problem would become more prominent where color pigments are employed in these photo-curing type inkjet inks.
Once the viscosity, surface tension, elastic force, etc. of the ink fluctuate on account of the deterioration of dispersibility of pigment as described above, it may lead to the turbulence in trajectory configuration of ink, printing error, linear missing of ink delivery, the deterioration of printing reproducibility, or in the worst case, may lead to a critical state such as the failure of delivery of ink, the clogging of ink, etc. Therefore, this problem is very serious.